The present invention concerns the field of electromagnetic radiation beams used for different types of measurement and visualization. The invention is applicable notably to X-ray imaging or processing devices, for example, in the medical field.
A radiology apparatus generally comprises means for an X-ray emission having equipped with an X-ray tube and a collimator, means for receiving the X-ray emissions separated from the means for emission by a distance sufficient to place there an object that it is desired to study. The collimator serves to determine the solid angle of aperture of the X-ray beam. The X-ray beam can thus be limited to the surface of the receiver. The collimator can also serve to further reduce the solid angle of the beam in order to limit it to a particular zone of interest of the object that is studied or processed, which makes it possible to prevent other parts of the object from being subjected to X-rays. The collimator can include a diaphragm made according to the principle of the diaphragm of a camera of articulated moving plane type. A diaphragm whose attenuating material consists of a deformable solid or of a fluid in a chamber is also disclosed in FR-A-2,601,544.
In addition, a radiology apparatus further comprises an electronic control unit for the X-ray tube, collimator, receiver (provided, for example, with a scintillator), a high-voltage supply of the X-ray tube, etc.
Such an apparatus must be calibrated in order to attain a sufficient qualitative and quantitative precision of the structures observed on an image. The calibration is generally done by means of a phantom that is placed at the object site on the path of the X-ray beam. A phantom is an object separate from the apparatus and comprising parts opaque to X-rays arranged according to a geometry defined and known. An image of the phantom is acquired under the geometric conditions of an angle of incidence that it is sought to be calibrated. The projections of the characteristic points are then recognized in the image. Each characteristic point of the object is associated with its trace in the acquired image. The system of equation describing the projection supplying the image is inverted in the mathematical sense and the set of parameters of the projection is finally obtained for the given vantage point. A phantom and method of calibration of an X-ray imaging system is disclosed in FR-A-2,700,909 and EP-A-0,874,536.